On Wed, 10 Oct 2012, Dave Chinner wrote: > Date: Wed, 10 Oct 2012 06:39:08 +1100 > From: Dave Chinner <david@xxxxxxxxxxxxx> > To: Lukas Czerner <lczerner@xxxxxxxxxx> > Cc: xfs@xxxxxxxxxxx > Subject: Re: [PATCH] xfs: avoid underflow in xfs_ioc_trim() > > On Tue, Oct 09, 2012 at 02:15:45PM +0200, Lukas Czerner wrote: > > Currently if len argument in xfs_ioc_trim() is smaller than one BB > > (basic block) the 'end' variable underflow. Avoid that by bailing out if > > len is smaller than BB. > > > > Signed-off-by: Lukas Czerner <lczerner@xxxxxxxxxx> > > --- > > fs/xfs/xfs_discard.c | 7 ++++++- > > 1 files changed, 6 insertions(+), 1 deletions(-) > > > > diff --git a/fs/xfs/xfs_discard.c b/fs/xfs/xfs_discard.c > > index 69cf4fc..54dc58a 100644 > > --- a/fs/xfs/xfs_discard.c > > +++ b/fs/xfs/xfs_discard.c > > @@ -183,8 +183,12 @@ xfs_ioc_trim( > > range.minlen > XFS_FSB_TO_B(mp, XFS_ALLOC_AG_MAX_USABLE(mp))) > > return -XFS_ERROR(EINVAL); > > > > + end = BTOBBT(range.len); > > + if (0 == end) > > + goto out; > > Uggh. "if (end == 0)", please. Not a Star Wars fan then ? ;). Ok, I'll change that. > > + > > start = BTOBB(range.start); > > - end = start + BTOBBT(range.len) - 1; > > + end += start - 1; > > Better would be to check if end <= start. That way it also catches > start+len overflows. That's not possible. Even if range.start and range.len would be 2^64-1 (which is not possible for range.start) we always do the BTOBB conversion and ((2^64-1) / 512) * 2 always fits the _s64 type. > > > > minlen = BTOBB(max_t(u64, granularity, range.minlen)); > > > > if (end > XFS_FSB_TO_BB(mp, mp->m_sb.sb_dblocks) - 1) > > @@ -203,6 +207,7 @@ xfs_ioc_trim( > > if (last_error) > > return last_error; > > > > +out: > > range.len = XFS_FSB_TO_B(mp, blocks_trimmed); > > if (copy_to_user(urange, &range, sizeof(range))) > > return -XFS_ERROR(EFAULT); > > I think it should return EINVAL, not silently do nothing. If the > user application uses a loop that increments start/len based on the > returned amount of blocks trimmed, returning zero could send it into > an endless loop. That's not what the application would do. At least it would not set len to what's returned as number of blocs discarded, it does not make sense. However if user specify length smaller than what we're able to discard (in xfs it is BBSIZE if I am not mistaken?), then it probably make sense to return -EINVAL. It is similar situation of minlen, where we return -EINVAL if it is bigger than AG. However this will make it to fail at different threshold on different file system / block sizes so I am on the fence about it. What do you think, is it worth it ? Thanks! -Lukas > > Cheers, > > Dave. > _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
